1. Field of the Invention
This invention relates to a solid-state image pickup device with a plurality of photoelectric conversion regions arranged on a semiconductor substrate.
2. Description of the Related Art
A previously known digital camera uses a solid-state image pickup device including a plurality of first photoelectric conversion regions arranged in a row direction and a column direction orthogonal thereto on a semiconductor substrate and a plurality of micro-lenses located on the respective plurality of first photoelectric conversion lenses. In such a solid-state image pickup device, a plurality of second photoelectric conversion regions are arranged between the adjacent micro-lenses to synthesize image pick-up signals from the first photoelectric conversion regions and those from the second photoelectric conversion regions, thereby extending the dynamic range of the digital camera (JP-A-10-74926).
In the solid-state image pickup device as disclosed in JP-A-10-74926, on the periphery, light obliquely comes so that shading occurs. In order to avoid the shading, conventionally, the size of each the photoelectric conversion regions is made larger at a farther distance from the center of the solid-state image pickup device, thereby reducing the shading. This measure for dealing with the shading intends to reduce the shading which is attributable to the optical system of the digital camera incorporating the solid-state image pickup device.
In the solid-state image pick-up device, since the plurality of photoelectric conversion regions are arranged at a high density on the semiconductor substrate, the interval between the micro-lenses corresponding to the plurality of photoelectric conversion regions is also very narrow. In the technique disclosed in JP-A-10-74926, the second photoelectric conversion regions are arranged between the adjacent micro-lenses. However, since the interval between the micro-lenses is very narrow, in addition to the above shading attributable to the optical system, the shading attributable to the micro-lenses will occur. Thus, with only the conventional measure for dealing with the shading, the shading cannot be sufficiently reduced. The shading which is attributable to the micro-lenses will be explained below.
FIG. 6 is a view showing a schematic section of the solid-state image pickup device disclosed in JP-A-10-74926. As seen from FIG. 6A, light beams a entering vertically from above the conventional solid-state image pick-up device come in each of micro-lenses 501, and pass through an opening plane 502 so that the light beams a are condensed by a first photodiode (PD) 503. The charges thus accumulated are transferred by a first vertical transfer unit 504. Further the light beams a pass through the opening plane 505 to enter a second PD 506 located between the micro-lenses 501. The charged thus accumulated are transferred by a second vertical transfer unit 507.
As seen from FIG. 6B, light beams b entering obliquely to the direction of arranging two micro-lenses 501, which sandwiches the second PD 506, from above the conventional solid-state image pick-up device come in each of micro-lenses 501, and pass through the opening plane 502 so that the light beams a are condensed by the first photodiode (PD) 503. The charges thus accumulated are transferred by a first vertical transfer unit 504. Further the light beams b pass through the opening plane 505 to enter the second PD 506. However a part of light beams b (arrow indicated by dotted line) cannot pass through the opening plane 505. This is true of the light beams c which come in symmetrically to the light beams b. On the other hand, most of the light beams entering in the direction of the second PD not sandwiched by the micro-lenses 501 (direction orthogonal to the direction indicated by arrow X) come in the second PD 506 because of absence of hindrance such as the micro-lenses.
As described above, where a PD is arranged in a narrow region between the two adjacent micro-lenses 501, the light beams b and c entering obliquely to the direction of the second PD 507 sandwiched by the micro-lenses 501 are concealed in their larger part by the shade of the micro-lens 501 so that a large quantity of light beams cannot pass through the opening plane 505. On the other hand, most of the light beams from the direction of the second PD 506 not sandwiched by the micro-lenses 501 comes in the second PD 506. As a result, the image pickup device is light in the direction of the second PD not sandwiched by the micro-lenses 501 and dark in the direction (X direction) of arranging the two micro-lenses 501 which sandwich the second PD 506, thus increasing the shading.
Thus, even if the conventional measure for dealing with the shading is performed, the signals produced from the second PDs 506 on the periphery of the solid-state image pick-up device are accompanied by the shading attributable to the micro-lenses. As regards the second PDs 506 on the periphery of the solid-state image pickup device, the measure for dealing with the shading is required for reducing both shading attributable to the optical system and shading attributable to the micro-lenses.